The invention relates to a method of and a device for moire reduction, and to an image display apparatus comprising a moire reduction device.
A display monitor operating under the raster scanning system repeats the line scanning of an electron beam by moving the resulting scanning lines in a direction substantially perpendicular to the line direction. In a usual raster scan, the lines are scanned in the horizontal direction while the lines succeed each other in the vertical direction. In the so called transposed scan, the lines are scanned in the vertical direction and succeed each other in the horizontal direction. In a cathode ray tube, the dot pitch of the fluorescent material on the screen of the CRT that can emit a fluorescence is determined by the aperture pitch of the shadow mask. Thus, in case of displaying a video pattern in which consecutive pixels in a line repeat in an ON and OFF sequence an interference with the aperture pitch of the shadow mask may occur, thereby causing a moire.
WO 97/09820 discloses a method of reducing the moire phenomenon upon display of a video signal on a display device by low-pass filtering the video signal. The low-pass filter has a cut-off frequency substantially corresponding to a maximum frequency of a baseband portion of the video signal to obtain a low-pass filtered video signal to be applied to the display device. It is a drawback of the prior art that a complex and expensive low pass filter is required to suppress all the harmonics of the baseband signal to a high degree to reach an optimum moire reduction, without attenuating the baseband signal to obtain an optimum sharpness of the displayed video.